Capsulitis...

...is the inflammation of the membrane that protects joints. It frequently affects the joint at the base of the second or third toes and the ball of the foot. It's more common in women; even if you don't wear high heels you'll probably still dance on your toes. Apparently most patients are found to be wearing shoes that are too small. It seems to be important not to ignore discomfort in that area: try to dance through it and it will get worse, and long-term inflammation can damage the joint and deform the foot. A friend and dance partner has just been put out of action for a while. Beware! Seek expert help early.